The invention relates to a gas and steam-turbine plant having a heat-recovery steam generator which is connected downstream of a gas turbine on a flue-gas side and heating surfaces of which are connected in a water/steam circuit of a steam turbine.
In a gas and steam-turbine plant, the heat contained in the expanded working medium or flue gas of the gas turbine is utilized to generate steam for a steam turbine. The heat transfer is effected in the heat-recovery steam generator which is connected downstream of the gas turbine on the flue-gas side and in which heating surfaces in the form of tubes or banks of tubes are disposed. The latter in turn are connected in a water/steam circuit of the steam turbine. The water/steam circuit normally contains a plurality of pressure stages, for example two pressure stages, each pressure stage having a preheating and an evaporating heating surface.
It is normally necessary to cool the blades of the gas turbine of the gas-turbine plant. This is particularly the case when the blades are subjected to especially high thermal loading on account of inlet temperatures of a working medium in the gas turbine.
For cooling the blades, air may be extracted downstream of the air compressor of the gas-turbine plant. Due to the compression of the air in the air compressor, the air is heated to a high degree. Therefore cooling of the extracted compressor air may be necessary in order to ensure sufficient cooling of the blades of the gas turbine. A heat exchanger, to which the compressed air is admitted as a heating medium, may be provided for the cooling. On a secondary side, the heat exchanger may be configured as an evaporator, which is connected to the water/steam circuit of the steam turbine in order to recover the heat contained in the compressed air.
However, during the transport of the water/steam mixture from the evaporator to the heat-recovery steam generator, care should be taken to ensure that no separation of the two phases occurs. This is because back flows of the condensate may occur in the event of a phase separation. The back flows may cause condensation shocks in the lines and may thus lead to undesirable damage to the components.
It is accordingly an object of the invention to provide a gas and steam-turbine plant which overcomes the above-mentioned disadvantages of the prior art devices of this general type, in which, with especially little technical outlay, a separation of the two phases during the transport of the water/steam mixture from the evaporator to the heat-recovery steam generator is avoided in a reliable manner.
With the foregoing and other objects in view there is provided, in accordance with the invention, a gas and steam-turbine plant. The turbine plant contains a gas turbine having blades, a steam turbine, a water/steam circuit connected to the steam turbine, and a heat-recovery steam generator connected downstream of the gas turbine on a flue-gas side. The heat-recovery steam generator has heating surfaces connected in the water/steam circuit to the steam turbine. A steam collecting chamber having a number of sub-chambers connected to one another is provided. The sub-chambers are formed by a configuration of a number of bulkhead plates subdividing the steam collecting chamber. The turbine plant further has a water/steam drum and a plurality of feed pipes disposed in parallel on a steam side connecting the water/steam drum to the steam collecting chamber. Each of the sub-chambers of the steam collecting chamber are connected to one of the feed pipes. Additionally, the turbine plant has an evaporator connected to the gas turbine for feeding cooled air to the blades of the gas turbine for cooling the blades. The evaporator receives air as a heating medium and the evaporator cools the air resulting in the cooled air. The evaporator has a secondary side connected to the water/steam circuit and opens on an outlet side into the steam-collecting chamber.
For the gas and steam-turbine plant of the above-mentioned type, the object is achieved according to the invention by feeding air, being a heating medium, to the evaporator in which the air is cooled and then fed to the blades of the gas turbine for cooling the blades. The evaporator is connected on the secondary side to the water/steam circuit and in the process opens on the outlet side into a steam-collecting chamber, which is connected to a water/steam drum via a number of feed pipes connected in parallel on the steam side. The steam-collecting chamber has a number of sub-chambers, which are connected to one another and of which each is in each case assigned to a feed pipe. A number of bulkhead plates are advantageously disposed in the steam-collecting chamber in order to form the sub-chambers connected to one another. In this configuration, especially uniform feeding of the water/steam mixture located in the steam-collecting chamber to the individual feed pipes is ensured.
The invention is based on the idea that a separation of the two phases will not occur if, depending on the pressure, the flow velocity of the water/steam mixture does not fall below a certain value. In the process, the minimum velocity of the two-phase mixture, below which a phase separation may occur, depends on an inside diameter of the pipe through which the flow occurs. In this case, although a comparatively small inside diameter permits a comparatively high flow velocity without a phase separation occurring, it also limits the rate of flow through the feed pipe. In order to meet both requirements, a number of feed pipes having a comparatively small inside diameter are connected in parallel. In this case, a uniform admission to the feed pipes should be ensured. The uniform admission of steam to the feed pipes is ensured when approximately the same quantity of steam is assigned to each feed pipe and approximately the same steam pressure prevails in the region of the steam-collecting chamber that opens into the feed pipes. To this end, the steam-collecting chamber has a number of sub-chambers, which are connected to one another and to which in each case a feed pipe is assigned.
As extensive tests have shown, a flow velocity of the water/steam mixture of 35 m/s proves to be an especially favorable limit below which the flow velocity should not fall. This is because the pressure loss, the risk of erosion and corrosion and reliable prevention of the phase separation are in an especially balanced relationship to one another above this value. The feed pipes are therefore advantageously configured with regard to their number and their inside diameter di in such a way that, under all operating states of the plant, a flow velocity of the water/steam mixture flowing in them does not fall below 35 m/s.
The water/steam drum, for forming a circulation, is expediently connected on the inlet side and outlet side to an evaporator heating surface, which is disposed in the heat-recovery steam generator.
The advantages achieved with the invention relate in particular to the fact that, due to the parallel connection of the feed pipes, in which the sub-chamber of the steam-collecting chamber is assigned in each case to each feed pipe, a separation of the two phases of the water/steam mixture during the transport from the evaporator to the heat-recovery steam generator is prevented in an especially reliable manner. As a result, damage to corresponding components is reliably avoided, so that the gas and steam-turbine plant has an especially long service life. In addition, feedback of the heat energy contained in the air provided for cooling the blades into the steam-generating process of the plant is ensured in an especially favorable manner.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a gas and steam-turbine plant, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.